An FDA rule effective Aug. 5 states that foods may be labeled "gluten free" only if there's less than 20 parts per million of the protein. James Benet/iStockphoto hide caption

itoggle caption James Benet/iStockphoto

Wheat fields like this one could yield wheat with less zinc and iron in the future if they are exposed to higher levels of CO2, according to the journal Nature. Zaharov Evgeniy/iStockphoto.com hide caption

itoggle caption Zaharov Evgeniy/iStockphoto.com

The world is increasingly relying on a few dozen megacrops, like wheat and potatoes, for survival. Above, a wheat field in Arkansas. Danny Johnston/AP hide caption

itoggle caption Danny Johnston/AP

About 40 years ago wheat breeders introduced new varieties of wheat that helped farmers increase their grain yields. But scientists say those varieties aren't linked to the rise in celiac disease. Karen Bleier/AFP/Getty Images hide caption

itoggle caption Karen Bleier/AFP/Getty Images

Wheat grows in a test field at Oregon State University in Corvallis. Some scientists believe that there's a chance that genetically modified wheat found in one farmer's field in May is still in the seed supply. Natalie Behring/Bloomberg via Getty Images hide caption

itoggle caption Natalie Behring/Bloomberg via Getty Images